The invention relates to a method for assembling a single-flow turbomolecular vacuum pump in which components such as the rotor, the drive motor and the rotor shaft, supported by antifriction bearings, are accommodated in a casing. The invention further relates to a pump assembled by that method.
In a prior-art method, a turbomolecular pump is initially assembled without its stator. Following this, the rotating system is rough-balanced under atmospheric pressure at speeds of up to a few thousand revolutions per minute. As used herein, balance always refers to the art of rotationally balancing rotary parts. Then the pump is completely assembled, provided with a blind flange, and placed in operation so that the balancing of the rotor can be continued under vacuum conditions and at rated speed. This calls for a number of balancing operations since the point of unbalance of the rotating parts of a completely assembled turbomolecular pump cannot always be pinpointed. The reasons for this are the necessary resilient mounting of the rotating system in the pump casing and the phase shifts resulting therefrom. After each balancing operation the pump must be stopped and opened to permit the unbalance to be corrected on the rotating system, by drilling, for example.
Besides, measuring and removing unbalance requires costly equipment. This is why turbomolecular vacuum pumps can be balanced only on the manufacturer's premises. Pumps which are already in service on a user's premises and on which maintenance or repair work is to be performed must therefore be shipped back to the manufacturer every time, so that the user has to contend with long outages.